This is a continuation-in-part of U.S. patent application Ser. No. 07/149,690 filed Jan. 28, 1988 and now abandoned.
Generally speaking, roadside signs having lighting elements for illuminating them at night are more effective than signs which reflect light only, for example, from passing vehicles with passengers for whom the signs are intended. However, the requirement of providing lighting for such signs greatly limits the locations where the signs can be placed since a suitable power source must be provided for the lighting element.
In addition, it is of course desirable to minimize both installation costs and operating costs for the lighted signs.
The prior art has provided a variety of illumination systems for such signs or for similar locations requiring illumination. For example, U.S. Pat. No. 4,319,310 issued Mar. 9, 1982 to Kingsley disclosed a sign assembly with a self-contained solar array for operating an illuminating lamp or lamps for the sign. U.S. Pat. No. 4,283,657 issued Aug. 11, 1981 to Gordon, et al. disclosed an illuminating system for illuminating exit signs or the like. U.S. Pat. No. 4,200,904 issued Apr. 29, 1980 to Doan disclosed a solar powered street lighting system totally independent of any external power supply.
Other prior art references have provided various control systems for operating illuminating components such as those referred to above. For example, U.S. Pat. No. 3,720,913 issued Mar. 13, 1973 to Bradford disclosed a courtesy display operating under poor ambient light conditions for notifying a motorist leaving a private service area without turning on his headlights. The display system was initiated by a proximity sensor or trip plate operated by the car itself. Once operation was initiated, the display system included a photocell arranged in the path of the car leaving the service area to determine if its lights were on.
Similarly, U.S. Pat. No. 4,384,317 issued May 17, 1983 to Stackpole disclosed a solar powered lighting system including a light element, battery, photovoltaic panel, timer and various components to properly charge the battery and provide switching functions. This patent is generally representative of a number of other references disclosing solar powered lighting systems.
U.S. Pat. No. 4,249,160 issued Feb. 3, 1981 to Chilvers disclosed a light activated control system mounted on a vehicle for operating warning lights on the vehicle when it is parked at night, in response to light above a selected intensity level from an approaching vehicle. Here again, the warning system was dependent upon light from the approaching vehicle directly impinging upon a sensor for operating the warning system.